Serotype changes in adult invasive pneumococcal infections in Portugal did not reduce the high fraction of potentially vaccine preventable infections

Abstract

We determined the serotype and antimicrobial susceptibility of 1100 isolates responsible for adult invasive pneumococcal infections (IPD) in Portugal between 2006 and 2008. Serotypes 3 (13%), 1 (12%), 7F (11%), 19A (10%) and 14 (7%) were the most frequent causes of IPD and the two later serotypes accounted for the majority of erythromycin and penicillin nonsusceptible isolates. Serotype 1 was associated with younger adults whereas serotype 3 was associated with older adults. Despite the availability of the 23-valent polysaccharide vaccine (PPV23) in Portugal since 1996, the proportion of PPV23 preventable IPD remained stable and above 80%. Comparing with previous data from Portugal, we showed a continued decline of the serotypes included in the 7-valent conjugate vaccine (PCV7) in adult IPD and a rise of serotypes included in the 13-valent conjugate vaccine, increasing its potential coverage of adult IPD to 70% in 2008. Penicillin non-susceptibility remained stable (17%) whereas erythromycin resistance (18%) has continued to rise in the post-PCV7 years.